midnightg35x
10+ year member
RF Amp Design Engineer
Caps can discharge their energy much quicker than a battery. This is pretty much the only reason for a capacitor. They certainly are not going to win any competitions on which can hold more energy (cap vs battery). Peaks in music are just that... peaks. They do not last that long and the car's charging system can recharge a cap fairly quickly during non-peaks without really straining itself.^ yeppers they hold voltage for a second until the bass hits and drains them and has to stop hitting to regain a charge. Why would you rather buy a used cap than a batt. you can check the voltage of a used batt.
As for a used battery vs a used capacitor, the answer on that one is lifetime. A battery has a finite lifetime MUCH shorter than that of a capacitor. I would have no problem buying a 3 year old capacitor, but I would be leary of almost any battery that has seen 3 years of constant use (especially in a car audio environment).